A few weeks ago, after about 10 minutes of normal operation/driving, the CEL came on at highway speed and the car started missing under very light acceleration. If not accelerating it ran as smooth as normal. CEL stayed on for the approximately 10 to 15 minutes it took to get the car back home.

Restarted it the following day, CEL did not come on. Drove it for 20 minutes and the CEL did not come back on but the miss persists, but now it requires heavier acceleration to make it miss. Perfectly fine at steady cruise and light/moderate acceleration. Have driven it a dozen times since and still no CEL, but still missing as above. Engine starts just fine, runs smooth, not over heating, no strange sounds at all.

Question - even though the CEL has remained off, was the code saved from when it did come on?

 

Pretty sure it did store it. I'm no mechanic but it possibly sounds like a random misfire.

 

Thanks, DD, my guess also is that the code is still there.

Yes, definitely sounds and feels like a misfire, and I can reproduce it anytime I drive the car. But the CEL came on only that one time.

 

If you haven't done so, buy an inexpensive code reader from Amazon. I use a $30 one that's saved me a lot of money. Good luck!

 

I actually have a code reader, an Innovate LM-2, that I bought years ago primarily to tune the A/F ratio on my classic car.

Hooked it up to the 550, it successfully connected to the CAN bus protocol, but there were zero DTC's stored. Hate to just start throwing parts at it. Car has only 45k miles on it but I'll start with the spark plugs.

 

It's probably a good place to start. I don't know how many miles your car has, but I believe MB recommends plugs at 60K anyway. Good luck!